Method for operating terminal in wireless communication system, and terminal using said method

ABSTRACT

Provided is a method for operating a terminal in a wireless communication system and a terminal using said method. The method comprises the steps of: transmitting, to a network, information indicating transmission necessity of a terminal-to-terminal control message; receiving, from the network, a setting regarding transmission of the terminal-to-terminal control message; and transmitting, to another terminal, the terminal-to-terminal control message on the basis of the setting.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2015/008222, filed on Aug. 5, 2015,which claims the benefit of U.S. Provisional Application No. 62/033,612filed on Aug. 5, 2014, the contents of which are all hereby incorporatedby reference herein in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to wireless communication and, moreparticularly, to a method of transmitting a control message for D2Doperation by a terminal to other terminal under control by a network andthe terminal using the method.

Related Art

In an International Telecommunication Union Radio communication sector(ITU-R), a standardization of International Mobile Telecommunication(IMT)-Advanced being a next mobile communication system after a thirdgeneration has been performed. The IMT-Advanced is aimed at supportingan Internet Protocol (IP) based multi-media service with a datatransmission rate of 1 Gbps in a stop and low speed moving state and adata transmission rate of 1 Gbps in a high speed moving state.

A 3rd Generation Partnership Project (3GPP) is preparing LTE-Advanced(LTE-A) being an improved one of Long Term Evolution (LTE) based on anOFDMA (Orthogonal Frequency Division Multiple Access)/SC-FDMA (SingleCarrier-Frequency Division Multiple Access) transmission scheme as asystem standard satisfying requirements of IMT-Advanced. The LTE-A isone important candidate for IMT-Advanced.

In recent years, there is growing interest in a Device-to-Device (D2D)technology performing direct communication between devices. Inparticular, the D2D is attracting attention as a communicationtechnology for a public safety network. A commercial communicationnetwork has been rapidly changed to the LTE but a current public safetynetwork is based on a 2G technology in a collision problem and a costside with an existing communication standard. Request for the technologyclearance and an improved service induces an effort to improve thepublic safety network.

The public safety network has high service requirements (reliability andsecurity) as compared with a commercial communication network. Inparticular, when coverage of cellular communication is insufficient oris not used, there is a need for direct signal transmission/receptionbetween devices, that is, a D2D operation.

The D2D operation may be signal transmission/reception between adjacentdevices to have various advantages. For example, a D2D terminal mayperform data communication with a high transmission rate and low delay.Further, the D2D operation may distribute traffic converged in a basestation. If the D2D terminal serves as a relay, the D2D terminal mayserve to extend coverage of a base station.

Meanwhile, when it is attempted to perform the D2D operation between afirst terminal and a second terminal, the first terminal may be withinnetwork coverage, while the second terminal may be located out of thenetwork coverage. In this case, a resource pool for the D2D operationmay be configured to the first terminal, but it may not be configured tothe second terminal, and thus the first terminal needs to inform thesecond terminal of the resource pool. In general, the first terminalwithin the coverage needs to transmit the control message for the D2Doperation to the second terminal out of the coverage. In this case, in aprior art, it is not defined how the network controls the firstterminal.

SUMMARY OF THE INVENTION

Technical problem to be solved in the present invention is to provide anoperation method of terminal and the terminal using the method.

Provided is a method for operation of a user equipment (UE) in awireless communication system is provided. The method comprisestransmitting to a network, information informing of necessity oftransmission of a inter UE control message, receiving from the network,a configuration on the transmission of the inter UE control message and

transmitting, to other UE, the inter UE control message based on theconfiguration.

The inter UE control message may be an announcement with which aresource pool configured from the network to the UEs is informed to theother UE.

The resource pool may indicate resources being usable for a transmissionof D2D (device-to-device) signal within a coverage of the network.

The inter UE control message may be an announcement to inform the otherUE of information required to perform a relay function by the UE betweenthe other UE and the network.

The information informing of necessity of transmission of the inter UEcontrol message may be transmitted via a RRC (radio resource control)message.

The inter UE control message may be a control massage to be used for thepurpose of public safety.

The method further comprises transmitting to the network, informationindicating that the transmission of the inter UE control message is notrequired any more.

In another aspect, a user equipment (UE) is provided. The UE comprises aRadio Frequency (RF) unit that transmits and receives a radio signal anda processor operatively coupled to the RF unit, the processor that:transmits to a network, information informing of necessity oftransmission of a inter UE control message, receives from the network, aconfiguration on the transmission of inter UE control message andtransmits, to other UE, the inter UE control messages based on theconfiguration.

In accordance with the present invention, the terminal which enterswithin the network coverage informs the network that the control messagefor the D2D operation needs to be transmitted to other terminal out ofthe network coverage. Thus, the network may know that a particularterminal needs to transmit the control message for the D2D operation,and thus it may provide the particular terminal with an appropriateconfiguration. Under control/configuration of the network, theparticular terminal transmits the control message for the D2D operation,and thus an interference to be influenced within the network coveragemay be minimized over the case that the particular terminal randomlytransmits the control message for the D2D operation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system to which the presentinvention is applied.

FIG. 2 is a diagram showing a wireless protocol architecture for a userplane.

FIG. 3 is a diagram showing a wireless protocol architecture for acontrol plane.

FIG. 4 is a flowchart illustrating the operation of UE in the RRC idlestate.

FIG. 5 is a flowchart illustrating a procedure of establishing RRCconnection.

FIG. 6 is a flowchart illustrating an RRC connection reconfigurationprocedure.

FIG. 7 is a diagram illustrating an RRC connection re-establishmentprocedure.

FIG. 8 illustrates sub states where the terminal may have in an RRC_IDLEstate and a sub state transition process.

FIG. 9 illustrates a reference structure for a ProSe.

FIG. 10 illustrates arrangement examples of terminals performing ProSedirect communication and cell coverage.

FIG. 11 illustrates a user plane protocol stack for the ProSe directcommunication.

FIG. 12 illustrates a PC 5 interface for D2D discovery.

FIG. 13 illustrates an embodiment of a ProSe direct discovery procedure.

FIG. 14 illustrates another embodiment of a ProSe direct discoveryprocedure.

FIG. 15 represents the UE-NW relay.

FIG. 16 illustrated a case in which the present invention may beapplied.

FIG. 17 represents the D2D operation method of the terminal inaccordance with the method 1.

FIG. 18 represents the D2D operation method of the terminal inaccordance with the method 2.

FIG. 19 illustrates the case that the terminals in each of multiplecells inform the same terminal out of the coverage of differenttransmission resource pools.

FIG. 20 represents the operation method of the terminal in accordancewith the embodiment I.

FIG. 21 illustrates an example in which embodiment I is applied to theD2D operation.

FIG. 22 represents an operation method of the terminal in accordancewith an embodiment of the present invention.

FIG. 23 represents an operating method of the terminal in accordancewith another embodiment of the present invention.

FIG. 24 is a block diagram representing the terminal in which theembodiment of the present invention is implemented.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 shows a wireless communication system to which the presentinvention is applied. The wireless communication system may also bereferred to as an evolved-UMTS terrestrial radio access network(E-UTRAN) or a long term evolution (LTE)/LTE-A system.

The E-UTRAN includes at least one base station (BS) 20 which provides acontrol plane and a user plane to a user equipment (UE) 10. The UE 10may be fixed or mobile, and may be referred to as another terminology,such as a mobile station (MS), a user terminal (UT), a subscriberstation (SS), a mobile terminal (MT), a wireless device, etc. The BS 20is generally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as an evolved node-B (eNB), abase transceiver system (BTS), an access point, etc.

The BSs 20 are interconnected by means of an X2 interface. The BSs 20are also connected by means of an S1 interface to an evolved packet core(EPC) 30, more specifically, to a mobility management entity (MME)through S1-MME and to a serving gateway (S-GW) through S1-U.

The EPC 30 includes an MME, an S-GW, and a packet data network-gateway(P-GW). The MME has access information of the UE or capabilityinformation of the UE, and such information is generally used formobility management of the UE. The S-GW is a gateway having an E-UTRANas an end point. The P-GW is a gateway having a PDN as an end point.

Layers of a radio interface protocol between the UE and the network canbe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. Among them, a physical (PHY) layer belonging to the first layerprovides an information transfer service by using a physical channel,and a radio resource control (RRC) layer belonging to the third layerserves to control a radio resource between the UE and the network. Forthis, the RRC layer exchanges an RRC message between the UE and the BS.

FIG. 2 is a diagram showing a wireless protocol architecture for a userplane. FIG. 3 is a diagram showing a wireless protocol architecture fora control plane. The user plane is a protocol stack for user datatransmission. The control plane is a protocol stack for control signaltransmission.

Referring to FIGS. 2 and 3, a PHY layer provides an upper layer with aninformation transfer service through a physical channel. The PHY layeris connected to a medium access control (MAC) layer which is an upperlayer of the PHY layer through a transport channel. Data is transferredbetween the MAC layer and the PHY layer through the transport channel.The transport channel is classified according to how and with whatcharacteristics data is transferred through a radio interface.

Data is moved between different PHY layers, that is, the PHY layers of atransmitter and a receiver, through a physical channel. The physicalchannel may be modulated according to an Orthogonal Frequency DivisionMultiplexing (OFDM) scheme, and use the time and frequency as radioresources.

The functions of the MAC layer include mapping between a logical channeland a transport channel and multiplexing and demultiplexing to atransport block that is provided through a physical channel on thetransport channel of a MAC Service Data Unit (SDU) that belongs to alogical channel. The MAC layer provides service to a Radio Link Control(RLC) layer through the logical channel.

The functions of the RLC layer include the concatenation, segmentation,and reassembly of an RLC SDU. In order to guarantee various types ofQuality of Service (QoS) required by a Radio Bearer (RB), the RLC layerprovides three types of operation mode: Transparent Mode (TM),Unacknowledged Mode (UM), and Acknowledged Mode (AM). AM RLC provideserror correction through an Automatic Repeat Request (ARQ).

The RRC layer is defined only on the control plane. The RRC layer isrelated to the configuration, reconfiguration, and release of radiobearers, and is responsible for control of logical channels, transportchannels, and PHY channels. An RB means a logical route that is providedby the first layer (PHY layer) and the second layers (MAC layer, the RLClayer, and the PDCP layer) in order to transfer data between UE and anetwork.

The function of a Packet Data Convergence Protocol (PDCP) layer on theuser plane includes the transfer of user data and header compression andciphering. The function of the PDCP layer on the user plane furtherincludes the transfer and encryption/integrity protection of controlplane data.

What an RB is configured means a procedure of defining thecharacteristics of a wireless protocol layer and channels in order toprovide specific service and configuring each detailed parameter andoperating method. An RB can be divided into two types of a Signaling RB(SRB) and a Data RB (DRB). The SRB is used as a passage through which anRRC message is transmitted on the control plane, and the DRB is used asa passage through which user data is transmitted on the user plane.

If RRC connection is established between the RRC layer of UE and the RRClayer of an E-UTRAN, the UE is in the RRC connected state. If not, theUE is in the RRC idle state.

A downlink transport channel through which data is transmitted from anetwork to UE includes a broadcast channel (BCH) through which systeminformation is transmitted and a downlink shared channel (SCH) throughwhich user traffic or control messages are transmitted. Traffic or acontrol message for downlink multicast or broadcast service may betransmitted through the downlink SCH, or may be transmitted through anadditional downlink multicast channel (MCH). Meanwhile, an uplinktransport channel through which data is transmitted from UE to a networkincludes a random access channel (RACH) through which an initial controlmessage is transmitted and an uplink shared channel (SCH) through whichuser traffic or control messages are transmitted.

Logical channels that are placed over the transport channel and that aremapped to the transport channel include a broadcast control channel(BCCH), a paging control channel (PCCH), a common control channel(CCCH), a multicast control channel (MCCH), and a multicast trafficchannel (MTCH).

The physical channel includes several OFDM symbols in the time domainand several subcarriers in the frequency domain. One subframe includes aplurality of OFDM symbols in the time domain. An RB is a resourcesallocation unit, and includes a plurality of OFDM symbols and aplurality of subcarriers. Furthermore, each subframe may use specificsubcarriers of specific OFDM symbols (e.g., the first OFDM symbol) ofthe corresponding subframe for a physical downlink control channel(PDCCH), that is, an L1/L2 control channel. A Transmission Time Interval(TTI) is a unit time for subframe transmission.

The RRC state of UE and an RRC connection method are described below.

The RRC state means whether or not the RRC layer of UE is logicallyconnected to the RRC layer of the E-UTRAN. A case where the RRC layer ofUE is logically connected to the RRC layer of the E-UTRAN is referred toas an RRC connected state. A case where the RRC layer of UE is notlogically connected to the RRC layer of the E-UTRAN is referred to as anRRC idle state. The E-UTRAN may check the existence of corresponding UEin the RRC connected state in each cell because the UE has RRCconnection, so the UE may be effectively controlled. In contrast, theE-UTRAN is unable to check UE in the RRC idle state, and a Core Network(CN) manages UE in the RRC idle state in each tracking area, that is,the unit of an area greater than a cell. That is, the existence ornon-existence of UE in the RRC idle state is checked only for each largearea. Accordingly, the UE needs to shift to the RRC connected state inorder to be provided with common mobile communication service, such asvoice or data.

When a user first powers UE, the UE first searches for a proper cell andremains in the RRC idle state in the corresponding cell. The UE in theRRC idle state establishes RRC connection with an E-UTRAN through an RRCconnection procedure when it is necessary to set up the RRC connection,and shifts to the RRC connected state. A case where UE in the RRC idlestate needs to set up RRC connection includes several cases. Forexample, the cases may include a need to send uplink data for a reason,such as a call attempt by a user, and to send a response message as aresponse to a paging message received from an E-UTRAN.

A Non-Access Stratum (NAS) layer placed over the RRC layer performsfunctions, such as session management and mobility management.

In the NAS layer, in order to manage the mobility of UE, two types ofstates: EPS Mobility Management-REGISTERED (EMM-REGISTERED) andEMM-DEREGISTERED are defined. The two states are applied to UE and theMME. UE is initially in the EMM-DEREGISTERED state. In order to access anetwork, the UE performs a procedure of registering it with thecorresponding network through an initial attach procedure. If the attachprocedure is successfully performed, the UE and the MME become theEMM-REGISTERED state.

In order to manage signaling connection between UE and the EPC, twotypes of states: an EPS Connection Management (ECM)-IDLE state and anECM-CONNECTED state are defined. The two states are applied to UE andthe MME. When the UE in the ECM-IDLE state establishes RRC connectionwith the E-UTRAN, the UE becomes the ECM-CONNECTED state. The MME in theECM-IDLE state becomes the ECM-CONNECTED state when it establishes S1connection with the E-UTRAN. When the UE is in the ECM-IDLE state, theE-UTRAN does not have information about the context of the UE.Accordingly, the UE in the ECM-IDLE state performs procedures related toUE-based mobility, such as cell selection or cell reselection, without aneed to receive a command from a network. In contrast, when the UE is inthe ECM-CONNECTED state, the mobility of the UE is managed in responseto a command from a network. If the location of the UE in the ECM-IDLEstate is different from a location known to the network, the UE informsthe network of its corresponding location through a tracking area updateprocedure.

System information is described below.

System information includes essential information that needs to be knownby UE in order for the UE to access a BS. Accordingly, the UE needs tohave received all pieces of system information before accessing the BS,and needs to always have the up-to-date system information. Furthermore,the BS periodically transmits the system information because the systeminformation is information that needs to be known by all UEs within onecell. The system information is divided into a Master Information Block(MIB) and a plurality of System Information Blocks (SIBs).

The MIB may include a limited number of parameters that are mostessential and most frequently transmitted when other information isrequired to be obtained from a cell. UE first searches for an MIB afterdownlink synchronization. The MIB may include information, such as anSFN that supports downlink channel bandwidth, a PHICH configuration, andsynchronization and operates as a timing criterion and an eNB transmitantenna configuration. The MIB may be transmitted on a broadcast channel(BCH) through broadcasting.

SystemInformationBlockType1 (SIB1) of included SIBs is included in a“SystemInformationBlockType1” message and transmitted. The remainingSIBs other than the SIB1 is included in a system information message andtransmitted. To map the SIBs to the system information message may beflexibly configured by a scheduling information list parameter includedin the SIB1. In this case, each of the SIBs is included in a singlesystem information message, and only SIBs having the same schedulingrequirement value (e.g. cycle) may be mapped to the same systeminformation message. Furthermore, a SystemInformationBlockType2 (SIB2)is always mapped to a system information message corresponding to thefirst entry within the system information message list of a schedulinginformation list. A plurality of system information messages may betransmitted within the same cycle. The SIB1 and all the systeminformation messages are transmitted on a DL-SCH.

In addition to broadcast transmission, in an E-UTRAN, the SIB1 may bededicated-signaled in the state in which it includes a parameterconfigured like an existing configured value. In this case, the SIB1 maybe included in an RRC connection reconfiguration message andtransmitted.

The SIB1 includes information related to UE cell access, and defines thescheduling of other SIBs. The SIB1 may include information related tothe PLMN identifiers of a network, tracking area code (TAC) and a cellID, a cell barring status indicative of whether a cell is a cell onwhich camp-on is possible, the lowest reception level required within acell which is used as cell reselection criterion, and the transmissiontime and cycle of other SIBs.

The SIB2 may include radio resource configuration information common toall pieces of UE. The SIB2 may include information related to an uplinkcarrier frequency and uplink channel bandwidth, an RACH configuration, apage configuration, an uplink power control configuration, a soundingreference signal configuration, a PUCCH configuration supportingACK/NACK transmission, and a PUSCH configuration.

UE may apply a procedure for obtaining system information and detectinga change of system information to a primary cell (PCell) only. In asecondary cell (SCell), when a corresponding SCell is added, an E-UTRANmay provide all of pieces of system information related to an RRCconnection state operation through dedicated signaling. When systeminformation related to a configured SCell is changed, an E-UTRAN mayrelease an SCell that is taken into consideration and subsequently addthe changed system information. This may be performed along with asingle RRC connection reconfiguration message. An E-UTRAN may configureparameter values different from a value broadcasted within an SCell thathas been taken into consideration through dedicated signaling.

UE needs to guarantee the validity of a specific type of systeminformation, and such system information is called required systeminformation. The required system information may be defined as follows.

If UE is an RRC idle state: The UE needs to be guaranteed so that it hasthe valid versions of the MIB and the SIB1 in addition to the SIB2 toSIB8. This may comply with the support of a radio access technology(RAT) that is taken into consideration.

If UE is an RRC connection state: The UE needs to be guaranteed so thatit has the valid versions of the MIB, the SIB1, and the SIB2.

In general, the validity of system information may be guaranteed up to amaximum of 3 hours after the system information is obtained.

In general, service that is provided to UE by a network may beclassified into three types as follows. Furthermore, the UE differentlyrecognizes the type of cell depending on what service may be provided tothe UE. In the following description, a service type is first described,and the type of cell is described.

1) Limited service: this service provides emergency calls and anEarthquake and Tsunami Warning System (ETWS), and may be provided by anacceptable cell.

2) Suitable service: this service means public service for common uses,and may be provided by a suitable cell (or a normal cell).

3) Operator service: this service means service for communicationnetwork operators. This cell may be used by only communication networkoperators, but may not be used by common users.

In relation to a service type provided by a cell, the type of cell maybe classified as follows.

1) An acceptable cell: this cell is a cell from which UE may be providedwith limited service. This cell is a cell that has not been barred froma viewpoint of corresponding UE and that satisfies the cell selectioncriterion of the UE.

2) A suitable cell: this cell is a cell from which UE may be providedwith suitable service. This cell satisfies the conditions of anacceptable cell and also satisfies additional conditions. The additionalconditions include that the suitable cell needs to belong to a PublicLand Mobile Network (PLMN) to which corresponding UE may access and thatthe suitable cell is a cell on which the execution of a tracking areaupdate procedure by the UE is not barred. If a corresponding cell is aCSG cell, the cell needs to be a cell to which UE may access as a memberof the CSG.

3) A barred cell: this cell is a cell that broadcasts informationindicative of a barred cell through system information.

4) A reserved cell: this cell is a cell that broadcasts informationindicative of a reserved cell through system information.

FIG. 4 is a flowchart illustrating the operation of UE in the RRC idlestate. FIG. 4 illustrates a procedure in which UE that is initiallypowered on experiences a cell selection procedure, registers it with anetwork, and then performs cell reselection if necessary.

Referring to FIG. 4, the UE selects Radio Access Technology (RAT) inwhich the UE communicates with a Public Land Mobile Network (PLMN), thatis, a network from which the UE is provided with service (S410).Information about the PLMN and the RAT may be selected by the user ofthe UE, and the information stored in a Universal Subscriber IdentityModule (USIM) may be used.

The UE selects a cell that has the greatest value and that belongs tocells having measured BS and signal intensity or quality greater than aspecific value (cell selection) (S420). In this case, the UE that ispowered off performs cell selection, which may be called initial cellselection. A cell selection procedure is described later in detail.After the cell selection, the UE receives system informationperiodically by the BS. The specific value refers to a value that isdefined in a system in order for the quality of a physical signal indata transmission/reception to be guaranteed. Accordingly, the specificvalue may differ depending on applied RAT.

If network registration is necessary, the UE performs a networkregistration procedure (S430). The UE registers its information (e.g.,an IMSI) with the network in order to receive service (e.g., paging)from the network. The UE does not register it with a network whenever itselects a cell, but registers it with a network when information aboutthe network (e.g., a Tracking Area Identity (TAI)) included in systeminformation is different from information about the network that isknown to the UE.

The UE performs cell reselection based on a service environment providedby the cell or the environment of the UE (S440). If the value of theintensity or quality of a signal measured based on a BS from which theUE is provided with service is lower than that measured based on a BS ofa neighboring cell, the UE selects a cell that belongs to other cellsand that provides better signal characteristics than the cell of the BSthat is accessed by the UE. This procedure is called cell reselectiondifferently from the initial cell selection of the No. 2 procedure. Inthis case, temporal restriction conditions are placed in order for acell to be frequently reselected in response to a change of signalcharacteristic. A cell reselection procedure is described later indetail.

FIG. 5 is a flowchart illustrating a procedure of establishing RRCconnection.

UE sends an RRC connection request message that requests RRC connectionto a network (S510). The network sends an RRC connection establishmentmessage as a response to the RRC connection request (S520). Afterreceiving the RRC connection establishment message, the UE enters RRCconnected mode.

The UE sends an RRC connection establishment complete message used tocheck the successful completion of the RRC connection to the network(S530).

FIG. 6 is a flowchart illustrating an RRC connection reconfigurationprocedure. An RRC connection reconfiguration is used to modify RRCconnection. This is used to establish/modify/release RBs, performhandover, and set up/modify/release measurements.

A network sends an RRC connection reconfiguration message for modifyingRRC connection to UE (S610). As a response to the RRC connectionreconfiguration message, the UE sends an RRC connection reconfigurationcomplete message used to check the successful completion of the RRCconnection reconfiguration to the network (S620).

Hereinafter, a public land mobile network (PLMN) is described.

The PLMN is a network which is disposed and operated by a mobile networkoperator. Each mobile network operator operates one or more PLMNs. EachPLMN may be identified by a Mobile Country Code (MCC) and a MobileNetwork Code (MNC). PLMN information of a cell is included in systeminformation and broadcasted.

In PLMN selection, cell selection, and cell reselection, various typesof PLMNs may be considered by the terminal.

Home PLMN (HPLMN): PLMN having MCC and MNC matching with MCC and MNC ofa terminal IMSI.

Equivalent HPLMN (EHPLMN): PLMN serving as an equivalent of an HPLMN.

Registered PLMN (RPLMN): PLMN successfully finishing locationregistration.

Equivalent PLMN (EPLMN): PLMN serving as an equivalent of an RPLMN.

Each mobile service consumer subscribes in the HPLMN. When a generalservice is provided to the terminal through the HPLMN or the EHPLMN, theterminal is not in a roaming state. Meanwhile, when the service isprovided to the terminal through a PLMN except for the HPLMN/EHPLMN, theterminal is in the roaming state. In this case, the PLMN refers to aVisited PLMN (VPLMN).

When UE is initially powered on, the UE searches for available PublicLand Mobile Networks (PLMNs) and selects a proper PLMN from which the UEis able to be provided with service. The PLMN is a network that isdeployed or operated by a mobile network operator. Each mobile networkoperator operates one or more PLMNs. Each PLMN may be identified byMobile Country Code (MCC) and Mobile Network Code (MNC).

Information about the PLMN of a cell is included in system informationand broadcasted. The UE attempts to register it with the selected PLMN.If registration is successful, the selected PLMN becomes a RegisteredPLMN (RPLMN). The network may signalize a PLMN list to the UE. In thiscase, PLMNs included in the PLMN list may be considered to be PLMNs,such as RPLMNs. The UE registered with the network needs to be able tobe always reachable by the network. If the UE is in the ECM-CONNECTEDstate (identically the RRC connection state), the network recognizesthat the UE is being provided with service. If the UE is in the ECM-IDLEstate (identically the RRC idle state), however, the situation of the UEis not valid in an eNB, but is stored in the MME. In such a case, onlythe MME is informed of the location of the UE in the ECM-IDLE statethrough the granularity of the list of Tracking Areas (TAs). A single TAis identified by a Tracking Area Identity (TAI) formed of the identifierof a PLMN to which the TA belongs and Tracking Area Code (TAC) thatuniquely expresses the TA within the PLMN.

Thereafter, the UE selects a cell that belongs to cells provided by theselected PLMN and that has signal quality and characteristics on whichthe UE is able to be provided with proper service.

The following is a detailed description of a procedure of selecting acell by a terminal.

When power is turned-on or the terminal is located in a cell, theterminal performs procedures for receiving a service byselecting/reselecting a suitable quality cell.

A terminal in an RRC idle state should prepare to receive a servicethrough the cell by always selecting a suitable quality cell. Forexample, a terminal where power is turned-on just before should selectthe suitable quality cell to be registered in a network. If the terminalin an RRC connection state enters in an RRC idle state, the terminalshould selects a cell for stay in the RRC idle state. In this way, aprocedure of selecting a cell satisfying a certain condition by theterminal in order to be in a service idle state such as the RRC idlestate refers to cell selection. Since the cell selection is performed ina state that a cell in the RRC idle state is not currently determined,it is important to select the cell as rapid as possible. Accordingly, ifthe cell provides a wireless signal quality of a predetermined level orgreater, although the cell does not provide the best wireless signalquality, the cell may be selected during a cell selection procedure ofthe terminal.

A method and a procedure of selecting a cell by a terminal in a 3GPP LTEis described with reference to 3GPP TS 36.304 V8.5.0 (2009-03) “UserEquipment (UE) procedures in idle mode (Release 8)”.

A cell selection procedure is basically divided into two types.

The first is an initial cell selection procedure. In this procedure, UEdoes not have preliminary information about a wireless channel.Accordingly, the UE searches for all wireless channels in order to findout a proper cell. The UE searches for the strongest cell in eachchannel Thereafter, if the UE has only to search for a suitable cellthat satisfies a cell selection criterion, the UE selects thecorresponding cell.

Next, the UE may select the cell using stored information or usinginformation broadcasted by the cell. Accordingly, cell selection may befast compared to an initial cell selection procedure. If the UE has onlyto search for a cell that satisfies the cell selection criterion, the UEselects the corresponding cell. If a suitable cell that satisfies thecell selection criterion is not retrieved though such a procedure, theUE performs an initial cell selection procedure.

A cell selection criterion may be defined as in Equation 1 below.Following Equation 1 can be referred to as measurement for determiningwhether or not S-criterion is satisfied.Srxlev>0 AND Squal>0,where:Srxlev=Q _(rxlevmeas)−(Q _(rxlevmin) +Q _(rxlevminoffset))−P_(compensation),Squal=Q _(qualmeas)−(Q _(qualmin) +Q _(qualminoffset))  [Equation 1]

In this case, in Equation 1, the variables may be defined as in Table 1below.

TABLE 1 Srxlev Cell selection RX level value (dB) Squal Cell selectionquality value (dB) Q_(rxlevmeas) Measured cell RX level value (RSRP)Q_(qualmeas) Measured cell quality value (RSRQ) Q_(rxlevmin) Minimumrequired RX level in the cell (dBm) Q_(qualmin) Minimum required qualitylevel in the cell (dB) Q_(rxlevminoffset) Offset to the signalledQ_(rxlevmin) taken into account in the Srxlev evaluation as a result ofa periodic search for a higher priority PLMN while camped normally in aVPLMN Q_(qualminoffset) Offset to the signalled Q_(qualmin) taken intoaccount in the Squal evaluation as a result of a periodic search for ahigher priority PLMN while camped normally in a VPLMN Pcompensationmax(P_(EMAX) −P_(PowerClass), 0) (dB) P_(EMAX) Maximum TX power level anUE may use when transmitting on the uplink in the cell (dBm) defined asP_(EMAX) in [TS 36.101] P_(PowerClass) Maximum RF output power of the UE(dBm) according to the UE power class as defined in [TS 36.101]

Qrxlevminoffset and Qqualminoffset, that is, signaled values, are theresults of periodic discovery for a PLMN having higher priority while UEcamps on a normal cell within a VPLMN, and may be applied only when cellselection is evaluated. As described above, during the periodicdiscovery of a PLMN having higher priority, UE may perform cellselection evaluation using parameter values stored from another cell ofthe PLMN having such higher priority.

After the UE selects a specific cell through the cell selectionprocedure, the intensity or quality of a signal between the UE and a BSmay be changed due to a change in the mobility or wireless environmentof the UE. Accordingly, if the quality of the selected cell isdeteriorated, the UE may select another cell that provides betterquality. If a cell is reselected as described above, the UE selects acell that provides better signal quality than the currently selectedcell. Such a procedure is called cell reselection. In general, a basicobject of the cell reselection procedure is to select a cell thatprovides UE with the best quality from a viewpoint of the quality of aradio signal.

In addition to the viewpoint of the quality of a radio signal, a networkmay determine priority corresponding to each frequency, and may informthe UE of the determined priorities. The UE that has received thepriorities preferentially takes into consideration the priorities in acell reselection procedure compared to a radio signal quality criterion.

As described above, there is a method of selecting or reselecting a cellaccording to the signal characteristics of a wireless environment. Inselecting a cell for reselection when a cell is reselected, thefollowing cell reselection methods may be present according to the RATand frequency characteristics of the cell.

-   -   Intra-frequency cell reselection: UE reselects a cell having the        same center frequency as that of RAT, such as a cell on which        the UE camps on.    -   Inter-frequency cell reselection: UE reselects a cell having a        different center frequency from that of RAT, such as a cell on        which the UE camps on    -   Inter-RAT cell reselection: UE reselects a cell that uses RAT        different from RAT on which the UE camps

The principle of a cell reselection procedure is as follows.

First, UE measures the quality of a serving cell and neighbor cells forcell reselection.

Second, cell reselection is performed based on a cell reselectioncriterion. The cell reselection criterion has the followingcharacteristics in relation to the measurements of a serving cell andneighbor cells.

Intra-frequency cell reselection is basically based on ranking. Rankingis a task for defining a criterion value for evaluating cell reselectionand numbering cells using criterion values according to the size of thecriterion values. A cell having the best criterion is commonly calledthe best-ranked cell. The cell criterion value is based on the value ofa corresponding cell measured by UE, and may be a value to which afrequency offset or cell offset has been applied, if necessary.

Inter-frequency cell reselection is based on frequency priority providedby a network. UE attempts to camp on a frequency having the highestfrequency priority. A network may provide frequency priority that willbe applied by UEs within a cell in common through broadcastingsignaling, or may provide frequency-specific priority to each UE throughUE-dedicated signaling. A cell reselection priority provided throughbroadcast signaling may refer to a common priority. A cell reselectionpriority for each terminal set by a network may refer to a dedicatedpriority. If receiving the dedicated priority, the terminal may receivea valid time associated with the dedicated priority together. Ifreceiving the dedicated priority, the terminal starts a validity timerset as the received valid time together therewith. While the valid timeris operated, the terminal applies the dedicated priority in the RRC idlemode. If the valid timer is expired, the terminal discards the dedicatedpriority and again applies the common priority.

For the inter-frequency cell reselection, a network may provide UE witha parameter (e.g., a frequency-specific offset) used in cell reselectionfor each frequency.

For the intra-frequency cell reselection or the inter-frequency cellreselection, a network may provide UE with a Neighboring Cell List (NCL)used in cell reselection. The NCL includes a cell-specific parameter(e.g., a cell-specific offset) used in cell reselection.

For the intra-frequency or inter-frequency cell reselection, a networkmay provide UE with a cell reselection black list used in cellreselection. The UE does not perform cell reselection on a cell includedin the black list.

Ranking performed in a cell reselection evaluation procedure isdescribed below.

A ranking criterion used to give the priority of a cell is defined as inEquation 2.R _(s) =Q _(meas,s) +Q _(hyst) ,R _(n) =Q _(meas,n) −Q_(offset)  [Equation 2]

In Equation 2, Rs is the ranking criterion of a serving cell on which UEnow camps, Rn is the ranking criterion of a neighboring cell, Qmeas,s isthe quality value of the serving cell measured by the UE, Qmeas,n is thequality value of the neighboring cell measured by the UE, Qhyst is ahysteresis value for ranking, and Qoffset is an offset between the twocells.

In Intra-frequency, if UE receives an offset “Qoffsets,n” between aserving cell and a neighbor cell, Qoffset=Qoffsets,n. If UE does notQoffsets,n, Qoffset=0.

In Inter-frequency, if UE receives an offset “Qoffsets,n” for acorresponding cell, Qoffset=Qoffsets,n+Qfrequency. If UE does notreceive “Qoffsets,n”, Qoffset=Qfrequency.

If the ranking criterion Rs of a serving cell and the ranking criterionRn of a neighbor cell are changed in a similar state, ranking priorityis frequency changed as a result of the change, and UE may alternatelyreselect the twos. Qhyst is a parameter that gives hysteresis to cellreselection so that UE is prevented from to alternately reselecting twocells.

UE measures RS of a serving cell and Rn of a neighbor cell according tothe above equation, considers a cell having the greatest rankingcriterion value to be the best-ranked cell, and reselects the cell.

In accordance with the criterion, it may be checked that the quality ofa cell is the most important criterion in cell reselection. If areselected cell is not a suitable cell, UE excludes a correspondingfrequency or a corresponding cell from the subject of cell reselection.

Hereinafter, radio link failure (RLF) will be described.

UE continues to perform measurements in order to maintain the quality ofa radio link with a serving cell from which the UE receives service. TheUE determines whether or not communication is impossible in a currentsituation due to the deterioration of the quality of the radio link withthe serving cell. If communication is almost impossible because thequality of the serving cell is too low, the UE determines the currentsituation to be an RLF.

If the RLF is determined, the UE abandons maintaining communication withthe current serving cell, selects a new cell through cell selection (orcell reselection) procedure, and attempts RRC connectionre-establishment with the new cell.

In the specification of 3GPP LTE, the following examples are taken ascases where normal communication is impossible.

-   -   A case where UE determines that there is a serious problem in        the quality of a downlink communication link (a case where the        quality of a PCell is determined to be low while performing RLM)        based on the radio quality measured results of the PHY layer of        the UE    -   A case where uplink transmission is problematic because a random        access procedure continues to fail in the MAC sublayer.    -   A case where uplink transmission is problematic because uplink        data transmission continues to fail in the RLC sublayer.    -   A case where handover is determined to have failed.    -   A case where a message received by UE does not pass through an        integrity check.

An RRC connection re-establishment procedure is described in more detailbelow.

FIG. 7 is a diagram illustrating an RRC connection re-establishmentprocedure.

Referring to FIG. 7, UE stops using all the radio bearers that have beenconfigured other than a Signaling Radio Bearer (SRB) #0, and initializesa variety of kinds of sublayers of an Access Stratum (AS) (S710).Furthermore, the UE configures each sublayer and the PHY layer as adefault configuration. In this procedure, the UE maintains the RRCconnection state.

The UE performs a cell selection procedure for performing an RRCconnection reconfiguration procedure (S720). The cell selectionprocedure of the RRC connection re-establishment procedure may beperformed in the same manner as the cell selection procedure that isperformed by the UE in the RRC idle state, although the UE maintains theRRC connection state.

After performing the cell selection procedure, the UE determines whetheror not a corresponding cell is a suitable cell by checking the systeminformation of the corresponding cell (S730). If the selected cell isdetermined to be a suitable E-UTRAN cell, the UE sends an RRC connectionre-establishment request message to the corresponding cell (S740).

Meanwhile, if the selected cell is determined to be a cell that uses RATdifferent from that of the E-UTRAN through the cell selection procedurefor performing the RRC connection re-establishment procedure, the UEstops the RRC connection re-establishment procedure and enters the RRCidle state (S750).

The UE may be implemented to finish checking whether the selected cellis a suitable cell through the cell selection procedure and thereception of the system information of the selected cell. To this end,the UE may drive a timer when the RRC connection re-establishmentprocedure is started. The timer may be stopped if it is determined thatthe UE has selected a suitable cell. If the timer expires, the UE mayconsider that the RRC connection re-establishment procedure has failed,and may enter the RRC idle state. Such a timer is hereinafter called anRLF timer. In LTE spec TS 36.331, a timer named “T311” may be used as anRLF timer. The UE may obtain the set value of the timer from the systeminformation of the serving cell.

If an RRC connection re-establishment request message is received fromthe UE and the request is accepted, a cell sends an RRC connectionre-establishment message to the UE.

The UE that has received the RRC connection re-establishment messagefrom the cell reconfigures a PDCP sublayer and an RLC sublayer with anSRB1. Furthermore, the UE calculates various key values related tosecurity setting, and reconfigures a PDCP sublayer responsible forsecurity as the newly calculated security key values. Accordingly, theSRB 1 between the UE and the cell is open, and the UE and the cell mayexchange RRC control messages. The UE completes the restart of the SRB1,and sends an RRC connection re-establishment complete message indicativeof that the RRC connection re-establishment procedure has been completedto the cell (S760).

In contrast, if the RRC connection re-establishment request message isreceived from the UE and the request is not accepted, the cell sends anRRC connection re-establishment reject message to the UE.

If the RRC connection re-establishment procedure is successfullyperformed, the cell and the UE perform an RRC connection reconfigurationprocedure. Accordingly, the UE recovers the state prior to the executionof the RRC connection re-establishment procedure, and the continuity ofservice is guaranteed to the upmost.

FIG. 8 illustrates sub states where the terminal may have in an RRC_IDLEstate and a sub state transition process.

Referring to FIG. 8, a terminal performs an initial cell selectionprocess (S801). The initial cell selection process may be performed whenthere is no stored cell information with respect to the PLMN or asuitable cell is not found.

If the suitable cell is not found in the initial cell selection process,the terminal transitions to an any cell selection state (S802). Theoptional cell selection state represents a state which does not camp onin both of a suitable cell and an acceptable cell. The optional cellselection state is a state attempted by the terminal in order to find anacceptable cell of an optional PLMN which may camp on. When the terminalfinds no cells which may camp on, the terminal is continuouslymaintained in an optional cell selection state until the acceptable cellis found.

If the suitable cell is found in the initial cell selection process, thestate transits to a normal camp state (S803). The normal camp staterepresents a state which camps on the normal cell. A paging channel isselected according to information given through system information tomotor, and an evaluation process for cell reselection may be performed.

In the normal camp state (S803), if a cell reselection evaluationprocess (S804) is caused, the cell reselection evaluation process (S804)is performed. If a suitable cell is found in the cell reselectionevaluation process (S804), the terminal again transits to the normalcamp state (S803).

If an acceptable cell is found in the any cell selection state (S802),the terminal transits to an any cell camped state (S805). The any cellcamped state (S805) represents a state of camping on an acceptable cell.

In the any cell camped state (S805), the terminal may select a pagingchannel according to information given through system information tomonitor, and may perform a cell reselection evaluation process (S806).If the acceptable cell is not found in the cell reselection evaluationprocess (S806), the terminal transits the any cell selection state(S802).

Hereinafter, a D2D operation will be described. In the 3GPP LTE-A, aservice related to the D2D operation refers to Proximity based Services(ProSe). Hereinafter, the ProSe is an equivalent concept with the D2Doperation and the ProSe may be compatibly used with the D2D operation.The ProSe is now described.

The ProSe includes ProSe direct communication and ProSe directdiscovery. The ProSe direct communication presents communicationperformed by two or more adjacent terminals. The terminals may performcommunication using a protocol of a user plane. A ProSe-enabled UE meansa UE for supporting a process related to requirements of the ProSe.Unless otherwise defined, the ProSe-enabled UE includes both of a publicsafety UE and a non-public safety UE. The public safety UE represents aUE for supporting both of a public safety specified function and theProSe process. The non-public safety UE is a terminal which supports theProSe process but does not support the public safety specified function.

The ProSe direct discovery is a process where the ProSe-enabled UEdiscovers another ProSe-enabled UE. In this case, only ability of thetwo ProSe-enabled UEs is used. An EPC-level ProSe discovery signifies aprocess where an EPC determines whether 2 ProSe enable terminals areclosed to each other, and reports the close state thereof the two ProSeenabled terminals.

Hereinafter, the ProSe direct communication may refer to D2Dcommunication, and the ProSe direct discovery may refer to D2Ddiscovery.

FIG. 9 illustrates a reference structure for a ProSe.

Referring to FIG. 9, the reference structure for a ProSe includes aplurality of terminals having E-UTRAN, EPC, and ProSe applicationprogram, a ProSe application (APP) server, and a ProSe function.

An EPC is a representative example of the E-UTRAN. The EPC may includean MME, an S-GW, a P-GW, a policy and charging rules function (PCRF),and a home subscriber server (HSS).

The ProSe application server is a user of ProSe in order to make anapplication function. The ProSe application server may communicate withan application program in the terminal. The application program in theterminal may use a ProSe ability to make an application function.

The ProSe function may include at least one of following functions butis not limited thereto.

-   -   Interworking via a reference point towards the 3rd party        applications    -   Authorization and configuration of the UE for discovery and        direct communication)    -   Enable the function of the EPC level ProSe discovery    -   ProSe related new subscriber data and handling of data storage,        and also handling of ProSe identities    -   Security related function    -   Provide control towards the EPC for policy related function    -   Provide function for charging (via or outside of EPC, e.g.,        offline charging))

Hereinafter, a reference point and a reference interface will bedescribed in a reference structure for the ProSe.

-   -   PC1: a reference point between a ProSe application program in        the terminal and a ProSe application program in a ProSe        application server. The PC1 is used to define signaling        requirements in an application level.    -   PC2: is a reference point between the ProSe application server        and a ProSe function. The PC2 is used to define an interaction        between the ProSe application server and a ProSe function. An        application data update of a ProSe database of the ProSe        function may be an example of the interaction.    -   PC3: is a reference point between the terminal and the ProSe        function. The PC3 is used to define an interaction between the        terminal and the ProSe function. Configuration for ProSe        discovery and communication may be an example of the        interaction.    -   PC4: is a reference point between an EPC and the ProSe function.        The PC4 is used to define an interaction between the EPC and the        ProSe function. The interaction lay illustrate when a path for        1:1 communication or a ProSe service for real time session        management or mobility management are authorized.    -   PC5: is a reference point to use control/user plane for        discovery, communication, and relay between terminals, and 1:1        communication.    -   PC6: is a reference point to use a function such as ProSe        discovery between users included in different PLMNs.    -   SGi: may be used for application data and application level        control information exchange.

<ProSe Direct Communication (D2D Communication)>.

The ProSe direct communication is a communication mode where two publicsafety terminals may perform direct communication through a PC 5interface. The communication mode may be supported in both of a case ofreceiving a service in coverage of E-UTRAN or a case of separating thecoverage of E-UTRAN.

FIG. 10 illustrates arrangement examples of terminals performing ProSedirect communication and cell coverage.

Referring to FIG. 10(a), UEs A and B may be located outside of the cellcoverage. Referring to FIG. 10(b), the UE A may be located in the cellcoverage and the UE B may be located outside of the cell coverage.Referring to FIG. 10(c), both of UEs A and B may be located in the cellcoverage. Referring to FIG. 10(d), the UE A may be located in coverageof a first cell and the UE B may be in coverage of a second cell.

As described above, the ProSe direct communication may be performedbetween terminals which are provided at various positions.

FIG. 11 illustrates a user plane protocol stack for the ProSe directcommunication.

Referring to FIG. 11, the PC 5 interface includes a PDCH layer, a RLClayer, a MAC layer, and a PHY layer.

There may not be HARQ feedback in the ProSe direct communication. An MACheader may include the source layer-2 ID and the purpose layer-2 ID.

<Radio Resource Assignment for ProSe Direct Communication>.

A ProSe enable terminal may use following two modes with respect toresource assignments for the ProSe direct communication.

1. Mode 1

The mode 2 is a mode for receiving scheduling a resource for the ProSedirect communication from a base station. The terminal should be in aRRC_CONNECTED state according to the mode 1 in order to transmit data.The terminal requests a transmission resource to the base station, andthe base station schedules a resource for scheduling assignment and datatransmission. The terminal may transmit a scheduling request to the basestation and may transmit a Buffer Status Report (ProSe BSR). The basestation has data which the terminal will perform the ProSe directcommunication and determines whether a resource for transmitting thedata is required.

2. Mode 2

The mode 2 is a mode for selecting a direct resource. The terminaldirectly selects a resource for the ProSe direct communication from aresource pool. The resource pool may be configured by a network or maybe previously determined.

Meanwhile, when the terminal includes a serving cell, that is, when theterminal is in an RRC_CONNECTED state with the base station or islocated in a specific cell in an RRC_IDLE state, the terminal isregarded to be in coverage of the base station.

If the terminal is located outside of the coverage, only the mode 2 isapplicable. If the terminal is located in the coverage, the mode 1 orthe mode 2 may be used according to setting of the base station.

If there are no exceptional conditions, only when the base station isconfigured, the terminal may change a mode from the mode 1 to the mode 2or from the mode 2 to the mode 1.

<ProSe Direct Discovery (D2D Discovery)>

The ProSe direct discovery represents a process used to discover whenthe ProSe enabled terminal discovers other neighboring ProSe enabledterminal and refers to D2D direction discovery or D2D discovery. In thiscase, an E-UTRA wireless signal through the PC 4 interface may be used.Hereinafter, information used for the ProSe direct discovery refers todiscovery information.

FIG. 12 illustrates a PC 5 interface for D2D discovery.

Referring to FIG. 12, the PC 5 interface includes an MAC layer, a PHYlayer, and a ProSe Protocol layer being an upper layer. Permission forannouncement and monitoring of discovery information is handled in theupper layer ProSe Protocol. Contents of discovery information aretransparent to an access stratum (AS). The ProSe Protocol allows onlyvalid discovery information to be transferred to the AS forannouncement.

An MAC layer receives discovery information from the upper layer ProSeProtocol. An IP layer is not used for transmitting the discoveryinformation. The MAC layer determines a resource used in order toannounce the discovery information received from the upper layer. TheMAC layer makes and sends a protocol data unit (MAC PDU) to a physicallayer. An MAC header is not added.

There are two types of resource assignments for announcing the discoveryinformation.

1. Type 1

The type 1 is a method assigned so that resources for announcing thediscovery information are not terminal-specific and the base stationprovides resource pool configuration for announcing the discoveryinformation to the terminals. The configuration may be included in asystem information block (SIB) to be signaled in a broadcast scheme.Alternatively, the configuration may be included in a terminal specificRRC message to be provided. Alternatively, the configuration may bebroadcast-signaled or terminal-specific signaled of a different layerfrom the RRC message.

The terminal selects a resource from an indicated resource pool toannounce discovery information using the selected resource. The terminalmay announce discovery information through a resource optionallyselected during each discovery period.

2. Type 2

The type 2 is a method where resources for announcing the discoveryinformation are terminal-specifically assigned. A terminal in aRRC_CONNECTED state may request a resource for announcing a discoverysignal to the base station through a RRC signal. The base station mayassign a resource for announcing a discovery signal as an RRC signal. Aresource for monitoring the discovery signal in a configured resourcepool may be assigned in terminals.

With respect to a terminal in an RRC_IDLE state, a base station mayreport a type 1 resource pool for announcing the discovery signal as anSIB. Terminals where ProSe direct discovery is allowed use a type 1resource pool for announcing the discovery information in the RRC_IDLEstate. Alternatively, the base station 2) reports that the base stationsupports the ProSe direct discovery through the SIB but may not providethe resource for announcing the discovery information. In this case, theterminal should enter the RRC_CONNECTED state for announcing thediscovery information.

With respect to a terminal in an RRC_CONNECTED state, the base stationmay configure whether to use a type 1 resource pool or a type 2 resourcepool for announcing the discovery information through a RRC signal.

FIG. 13 illustrates an embodiment of a ProSe direct discovery procedure.

Referring to FIG. 13, it is assumed in a terminal A and a terminal Bthat a ProSe-enabled application program is operated, and the terminal Aand the terminal B are configured in a friend relationship to eachother, that is, a relationship capable of allowing D2D communicationwith each other in the application program. Hereinafter, the terminal Bmay be expressed as a friend of the terminal A. For example, theapplication program may be a social networking program. 3GPP Layerscorrespond to functions of an application program for using a ProSediscovery service regulated according to 3GPP.

A ProSe direct discovery between the terminal A and the terminal B mayperform a following procedure.

1. First, the terminal A performs regular application-Layercommunication with an application server. The above communication isperformed based on Application programming interface (API).

2. A ProSe enabled application program of the terminal A receives a listof application layer IDs having a friend relationship. The applicationlayer ID may generally be in the form of a network access ID. Forexample, an application layer ID of the terminal A may have a form suchas adam@example.com.

3. A terminal A requests private expression codes for a user and privateexpression codes for a friend of the user.

4. 3GPP layers transmit an expression code request to a ProSe server.

5. The ProSe server map application layer IDs provided from an operatoror a third application server to private expression codes. For example,an application layer ID such as adam@example.com. The mapping may beperformed based on parameters (e.g., mapping algorithms, key values, andthe like) received from an application service of the network.

6. The ProSe server responds the obtained expression codes to the 3GPPlayers. The 3GPP layers report that expression codes with respect to therequested application layer are successively received to the ProSeenabled application program. Further, a mapping table between theapplication layer IDs and the expression codes are generated.

7. The ProSe enabled application program requests the 3GPP layers tostart the discovery procedure. That is, when one of friends is locatedclose to the terminal A and direct communication may be performed, theProSe enabled application program attempts the discovery. 3GPP layersannounce a private expression code of the terminal A (that is,“GTER543$#2FSJ67DFSF” which is a private expression code ofadam@example.com in the above example). In mapping of an applicationlayer ID of a corresponding application program and the privateexpression code, the mapping relationship may be known by the previouslyreceived friends, and the mapping may be performed.

8. It is assumed that the terminal B is operating the same ProSe enabledapplication program as that of the terminal A, and the above steps 3 to6 may be executed. 3GPP layers included in the terminal B may performProSe discovery.

9. When the terminal B receives the above announce from the terminal A,the terminal B determines whether the private expression code includedin the announce is known by the terminal B or is mapped to anapplication layer ID. As illustrated in step 8, since the terminal Bperforms steps 3 to 6, the terminal B knows a private expression codewith respect to the terminal A, mapping of the private expression codeto the application layer ID, and which is a corresponding applicationprogram. Accordingly, the terminal B may discover the terminal B fromthe announce of the terminal A. The 3GPP layers in the terminal Bannounces that adam@example.com is discovered to the ProSe enableapplication program.

FIG. 13 illustrates a discovery procedure by taking into considerationthe terminals A and B, the ProSe server, and the application server.Only an operation side between the terminals A and B is described. Theterminal A transmits a signal called the announce (the procedure mayrefer to announcement), and the terminal B receives the announce todiscover the terminal A. That is, a discovery procedure of FIG. 13 in anoperation directly related to another terminal among operationsperformed by each terminal may refer to a single step discoveryprocedure may refer to a single step discovery procedure in a side ofone step.

FIG. 14 illustrates another embodiment of a ProSe direct discoveryprocedure.

In FIG. 14, it is assumed that the terminal 1 to the terminal 4 may beincluded in a specific group communication system enablers (GCSE) group.It is assumed that the terminal 1 is a discoverer and terminals 2, 3,and 4 are a discoveree. A terminal 5 is a terminal regardless of adiscovery procedure.

The terminal 1 and the terminals 2 to 4 may perform a followingoperation in a discovery procedure.

First, the terminal 1 broadcasts a targeted discovery request message(hereinafter referred to ‘discovery request message’ or ‘M1’) in orderto discover whether an optional terminal included in the GCSE group islocated around the terminal 1. The targeted discovery request messagemay include a unique application program group ID or a layer-2 group IDof the specific GCSE group. Further, the targeted discovery requestmessage may include a unique ID of the terminal 1, that is, anapplication program private ID. The targeted discovery request messagemay be received by the terminals.

The terminal 5 transmits no response messages. The terminals 2, 3, and 4included in the GCSE group transmit a targeted discovery responsemessage (hereinafter referred to as a discovery response message or M2)as a response to the targeted discovery request message. The targeteddiscovery response message may include a unique application programprivate ID of a terminal transmitting the message.

An operation of terminals in a ProSe discovery procedure illustrated inFIG. 14 will be described. A discoverer (UE 1) transmits the targeteddiscovery request message, and receives a targeted discovery responsemessage being a response thereto. In addition, if a discoveree (e.g., UE2) receives the targeted discovery request message, the discovereetransmits a targeted discovery response message as a response thereto.Accordingly, each terminal performs an operation a second step. In theabove side, a ProSe discovery procedure of FIG. 14 may refer to adiscovery procedure.

In addition to the discovery procedure illustrated in FIG. 14, if theterminal 1 (discoverer) transmits a discovery confirm message(hereinafter may refer to M3) as a response to the targeted discoveryresponse message, this may refer to a third step discovery procedure.

In the present invention, a network node such as a terminal may providerelay function for other network node. As for the terminal whichprovides relay function, it may be classified into a UE-NW relay, aUE-UE relay based on the any of network nodes among which the relayfunction is provided.

FIG. 15 represents the UE-NW relay.

Referring to FIG. 15, a second terminal 153 plays a role of the UE-NWrelay. That is, the second terminal 153 is a network node playing therole of the relay between a first terminal 152 located out of thenetwork coverage 154 and the network 151, and in this case the secondterminal 153 is referred to as the UE-NW relay.

In FIG. 15, as the first terminal 152 is located out of networkcoverage, if the second terminal 153 does not provide the relayfunction, then communications with the network 151 may not be performed.

The UE-NW relay 153 transmits and receives data via a communicationamong terminals (D2D operation) with the first terminal 151, and ittransmits and receives data via a general terminal-network communicationwith the network.

Now, the present invention is explained.

The terminal within the network coverage (the first terminal) mayperform a D2D operation with the terminal out of network coverage (thesecond terminal). In this case, the first terminal may inform the secondterminal of a control message for the D2D operation. This is referred toas an announcement in below.

As an example of the announcement, the first terminal may transmit thecontrol information informing the second terminal of at least one of aresource pool (capable of being used for a transmission of D2D signal),time/frequency synchronization information and timing informationconfigured from the network.

As other example of announcement, the first terminal may transmit relayoperation configuration information to the second terminal. As explainedin FIG. 15, the first terminal within the coverage may relaycommunication among the second terminal out of the network coverage,which is referred to as a D2D relay service. In this case, the secondterminal may be connected with the network via a link for the D2Doperation (which may be referred to as a sidelink or D2D link) with thefirst terminal. In this case, the first terminal may provide the relayoperation configuration information to provide the second terminal withthe D2D relay service.

As for the relay operation configuration information, for example, itmay include at least one of relay state information indicating whetherthe D2D relay service is provided by the first terminal (e.g.: relayservice initiation, relay service stop), information indicating an ID ofthe first terminal ID (e.g.: Layer 2 ID, an ID which is included in adestination of D2D message when the second terminal transmits a messageto the first terminal in D2D), information indicating a remaining amountof battery of the first terminal, information indicating a serving cellID (a physical layer Cell ID or a Global cell ID) of the first terminal,or information indicating PLMN information (primary PLMN and secondaryPLMN(s)) belonging to a serving cell of the first terminal.

As other example of the announcement, the first terminal may transmit tothe second terminal, information indicating a neighboring cellmeasurement result of the first terminal, information indicating themaximum bit rate to be provided to the second terminal by the firstterminal, or information indicating the minimum bit rate to be providedto the second terminal by the first terminal, etc.

As other example of the announcement, information indicating a servingcell measurement result of the first terminal, ‘configurationinformation on measurement and report’ to request a measurement reporton the side link from the first terminal to the second terminal,‘configuration information on measurement and report’ to request ameasurement report on the downlink from the first terminal to the secondterminal etc., may be transmitted.

As other example of the announcement, information to be requested toreport, from the first terminal to the second terminal, informationindicating a resource pool to be used by the second terminal, may betransmitted. A condition needs to be defined in order for the terminalto perform the announcement or to stop the announcement. The most directmethod is to configure for each terminal via a dedicated signal suchthat the network makes the terminal perform the announcement or stop theannouncement and thus the corresponding terminal would perform or stopthe announcement based on the dedicated signal.

However, according to a prior art, the network cannot know that whichone of multiple terminals wants to perform the announcement or whichterminal does not want to perform the announcement.

Further, after the terminal enters within the network coverage, then itattempts the RRC connection establishment, and if the network does notknow that the terminal needs to perform the announcement urgently forthe D2D operation, then the RRC connection establishment for theterminal may be delayed, and thus the announcement may be delayed and itmay result in a stop of the D2D operation.

In the present invention, it provides the operation method of theterminal and the terminal using the method, in which these issues may besolved.

FIG. 16 illustrated a case in which the present invention may beapplied.

Referring to FIG. 16, the first terminal (UE 1) located out of thenetwork coverage may move to enter within the network coverage. Then,the first terminal performs the D2D operation using the resourceconfigured by the network. If the first terminal performs the D2Doperation with the second terminal out of the network coverage, it maybe an issue which resource is used while the first terminal and thesecond terminal perform the D2D operation, and the following method 1 ormethod 2 may be used.

The method 1 is a method that the terminals out of the network coveragemodify the resource for the D2D operation to be matched to the resourcepool in the network coverage. The method 2 is a method that the terminalwithin the network coverage limits/modifies the resource for the D2Doperation to be matched to the resource pool used by the terminals outof the network coverage.

FIG. 17 represents the D2D operation method of the terminal inaccordance with the method 1.

Referring to FIG. 17, the first terminal receives from the network,resource pool information indicating resource pool B to be used for aD2D signal transmission within the network coverage (referred to as‘coverage’ in below). The resource pool information may include thesynchronization information required to use the resource pool and/or thetiming information required to identify the resource in time.

The first terminal may announce (inform) the resource pool B to thesecond terminal and the third terminal out of the coverage, and thesecond terminal and the third terminal performs the D2D operation withthe first terminal by using the resource pool B. The announcement may beperformed by an instruction from the network or may be performed by apredefined rule.

The first terminal may announce the transmission resource pool used forthe D2D signal transmission to the second terminal and the thirdterminal. If the second terminal and the third terminal receives theannouncement, then the resource used for the D2D signal transmission maybe replaced with the transmission resource pool indicated by theannouncement.

Further, the first terminal may announce a reception resource pool usedfor the D2D signal reception to the second terminal and the thirdterminal. The second terminal and the third terminal may monitor the D2Dsignal in the reception resource pool transferred by the announcement.The second terminal and the third terminal may extend its own receptionresource pool to include the reception resource pool transferred by theannouncement.

FIG. 18 represents the D2D operation method of the terminal inaccordance with the method 2.

Referring to FIG. 18, the network signals the transmission resource poolB to be usable for the D2D signal transmission. The second terminal andthe third terminal out of the coverage may use the transmission resourcepool A for the D2D signal transmission. As for the first terminal whichmoves from out of the coverage into the coverage, after it receives thesignal to configure the transmission resource pool B from the network,it configures the resource for the D2D signal transmission as theintersection of sets of transmission resource pool A, B

The first terminal, the second terminal and the third terminal maytransmit the D2D signal using the resource belonging to the intersectionof sets. When the first terminal transmits the D2D signal, it matchesits transmission timing to the reception resource pool of the terminalout of the coverage as the second terminal and the third terminal. Forexample, if the second terminal and the third terminal have itsreception resource pool allocated in the TDD (time division duplex)manner, then the first terminal should transmit the D2D signal byconsidering the UL-DL configuration of the second terminal and the thirdterminal.

If the method 2 is used, then the base station should know the receptionresource of the terminal out of the coverage, in which the terminalwithin the coverage may receive the information informing the receptionresource from the terminal out of the coverage, and terminal within thecoverage may transmit it to the base station.

The terminal within the coverage performs the announcement to theterminal out of the coverage in accordance with any one of the abovementioned method 1, 2. In general, the terminal within the coveragetransmits to the terminal out of the coverage, the control message toinform the resource (determined by the method 1 or 2) for the D2Doperation.

The terminal may perform the announcement once, or may perform theannouncement multiple times. For example, the terminal may periodicallyperform the announcement. Or, the terminal may perform the announcementby the number of times indicated by the network. Or, the terminal maycontinuously perform the announcement until it explicitly receives thesignal to stop the announcement from the network.

FIG. 19 illustrates the case that the terminals in each of multiplecells inform the same terminal out of the coverage of differenttransmission resource pools.

Referring to FIG. 19, the first terminal and the second terminal areterminals within the coverage in each of different cells. If the firstterminal and the second terminal inform the third terminal out of thecoverage of the transmission resource pool B, C respectively, then itmay be an issue that the third terminal should transmit the D2D signalusing which transmission resource pool. It may be assumed thattransmission resource pool B, C is not the completely overlappedresource pool, i.e. the same resource pool. In this case, whether thethird terminal uses which transmission resource pool, may be selectedfrom the perspective of the implementation of the terminal.

Embodiment I

As mentioned above, the terminal within the network coverage (the firstterminal) may perform the D2D operation with the terminal out of thenetwork coverage (the second terminal), in which the first terminal mayinform the second terminal of the control message for the D2D operation.However, in a prior art, since the network cannot know that the firstterminal wants to transmit the control message, it would be a difficultissue that the network controls the first terminal.

To solve the issue, in the present invention, it is proposed to informthe network that the terminal within the coverage is required totransmit the control message to the terminal out of the coverage.

When the first terminal informs the network of the necessity of theannouncement, it is available to indicate its purpose of theannouncement. To indicate its purpose of the announcement is todetermine whether the network configures the information to be includedin the announcement (the control message transmission) to the firstterminal, or determine whether the network permits the announcementbased on the purpose. To inform the network of the necessity or purposeof the announcement may be referred to as a request of the announcement.

The announcement request may be transmitted via sidelink UE informationRRC message to the network. Or, the announcement request e.g. which isincluded in RRC connection setup complete message, may be transmitted tothe network during the RRC connection establishment procedure.

If the network receives the announcement request from the terminal, thenthe network may indicate the announcement message transmission to theterminal. When the network indicates the announcement messagetransmission to the terminal, the information to be included in theannouncement message may be indicated or informed.

When the network indicates the announcement message transmission to theterminal, it may indicate the RRC state in which the announcement isavailable. For example, it may be indicated that the announcement isavailable only in a RRC connection state, or, it may be indicated thatthe announcement is available in both a RRC idle state and the RRCconnection state, or it may be indicated that the announcement isavailable only in the RRC idle state. When the network indicates theannouncement message transmission to the terminal, configurationinformation on start/continuation/stop of the announcement may beprovided as well. FIG. 20 represents the operation method of theterminal in accordance with the embodiment I.

Referring to FIG. 20, the terminal transmits to the network, theinformation informing necessity to transmit the control message among aterminal (S2010).

The control message among the terminal, for example, may include theinformation informing the terminal out of the coverage of the resourcepool configured for the D2D operation by the network.

The terminal receives from the network, a configuration on the controlmessage transmission among the terminal (S2020).

The terminal transmits the control message among the terminal to theother terminal based on the configuration (S2030). The other terminalmay be the terminal out of the network coverage.

FIG. 21 illustrates an example in which embodiment I is applied to theD2D operation.

Referring to FIG. 21, the first terminal enters from out of the coverageinto the coverage (S2101). The second terminal is located out of thecoverage.

The first terminal starts a RRC connection establishment procedure withthe base station (S2102).

The first terminal informs the base station (network) of the controlmessage among the terminal, e.g. necessity of resource pool announcement(S2103).

The base station provides the first terminal with a configurationrequired to transmit the control message among the terminal (S2104). Forexample, the configuration may be a configuration on the announcement ofresource pool, and it may inform that the announcement may betransmitted by using which resource.

The first terminal transmits the control message among the terminal,e.g., the resource pool announcement based on the configuration (S2105).The resource indicated by the resource pool announcement may indicatethe resource by the above mentioned method 1, method 2.

The second terminal coordinates the resource for the D2D operation basedon the control message among the terminal e.g. the resource poolannouncement.

FIG. 21 illustrates the case that the announcement performed by thefirst terminal informs the second terminal of the D2D resourceconfigured by the network (base station), but it is not limited thereto.

As mentioned above, the announcement may be to inform the secondterminal of the relay operation configuration information. In this case,the first terminal informs the network (base station) that it isrequired that the relay operation configuration information istransmitted, and receives from the network, a configuration to transmitthe relay operation configuration information. The first terminal maytransmit the relay operation configuration information to the secondterminal based on the configuration. The second terminal may knowwhether the D2D relay service of the first terminal is provided, thefirst terminal ID, the remaining amount of battery of the firstterminal, the serving cell ID (physical layer Cell ID or Global cell ID)of the first terminal, and PLMN to which the serving cell of the firstterminal is belonged etc. based on the relay operation configurationinformation transmitted by the first terminal. The second terminal maycommunicate with the network (base station) by utilizing the firstterminal as a relay.

When the terminal needs to announce the resource pool configured by thenetwork, the terminal may be in the RRC idle state. In this case, theterminal may transmit the RRC connection configuration request to thenetwork in order to transit to the RRC connection state. After thetransition into the RRC connection state, the network may configurewhether the terminal is informed that the announcement of resource poolis required. It is configured via a dedicated signal or a broadcastsignal.

The terminal may inform the network of necessity of the announcementduring the RRC connection establishment procedure. Or, the necessity ofthe announcement may be informed via the dedicated signal to thenetwork, after the RRC connection establishment procedure has beenfinished.

If the network receives from the terminal, the information indicatingthe necessity of the announcement, then it may configure the informationfor the resource pool to be announced.

Meanwhile, the information indicating the necessity of the announcementmay be transferred from a source cell to a target cell in a handoverprocess. Or, the information indicating the necessity of theannouncement may not be transferred from the source cell to the targetcell in the handover process. In this case, after handover has beenfinished, the target cell may transmit to the terminal, the informationindicating the necessity of the announcement.

The announcement on the resource pool used within the coverage may beperformed once, or may be performed multiple times. The announcementperformed once only is not sufficient to inform all terminals of aresource pool, and in this case the announcement may be performedmultiple times. If the announcement of resource pool is permitted by thenetwork, then it may be preferred that the announcement is performedmultiple times.

It may be an issue for implementation of the terminal how many and howoften announcements of resource pool may be performed. For example, ifthe announcement is configured, then terminal may continue to considerthat the announcement is permitted until it explicitly receives aconfiguration to stop the announcement, and the actual number ofannouncements is an issue for implementation of the terminal.

The terminal may periodically perform the announcement. The networkshould be able to configure for the terminal to stop the announcement atany time. If the network configures to stop the announcement, then theterminal immediately stop the announcement.

Meanwhile, though it is not illustrated in FIG. 21, the first terminalmay inform the network that the announcement is not required any more.This may be sort of announcement configuration release request.

Embodiment II

When the terminal makes a call to establish the RRC connection, theterminal provides the network with the information indicating a RRCconnection establishment cause. The network may perform a suitableaccess control for the terminal based on the RRC connectionestablishment cause.

The following table 2 illustrates an example of the RRC connectionrequest message including the RRC connection establishment cause value.

TABLE 2 -- ASN1START RRCConnectionRequest ::=     SEQUENCE {    criticalExtensions             CHOICE {        rrcConnectionRequest-r8             RRCConnectionRequest-r8-IEs,         criticalExtensionsFuture             SEQUENCE { }     } }RRCConnectionRequest-r8-IEs ::= SEQUENCE {     ue-Identity                InitialUE- Identity,     establishmentCause            EstablishmentCause,     spare                 BIT  STRING (SIZE (1)) } InitialUE-Identity ::=     CHOICE {     s-TMSI            S-TMSI,     randomValue             BIT STRING (SIZE (40)) }EstablishmentCause ::= ENUMERATED {     emergency, highPriorityAccess, mt-Access, mo-Signalling, mo-Data, delayTolerantAccess-v1020, spare2,spare1} -- ASN1STOP

In the above table 2, ‘EstablishmentCause’ is a field indicating the RRCconnection establishment cause. The value which the ‘EstablishmentCause’may have is in the following table.

TABLE 3 RRC  

  RRC  

No 1.

 (emergency) No 2.

 (highPriorityAccess) No 3. mt-access No 4. mo-signaling No 5. mo-dataNo 6. delayTolerantAccess

In the above table 3, the ‘emergency’ represents an urgent situation oran emergency situation. The ‘high priority access (highPriorityAccess)’represents that a priority of the access is high. The ‘mt-access,’ the‘mo (Mobile Originating)-signaling,’ the ‘mo-data,’ and‘delayTolerantAccess,’ may represent a Mobile Terminating access, aMobile Originating access of the terminal, an access for datatransmitted by the terminal, and an access tolerant to delay,respectively.

As shown in the table 3, there is no RRC connection establishment causevalue to identify between a ProSe-enabled public safety call (‘PS call’in below) and a ProSe-enabled non-public safety call (‘non-PS call’ inbelow.) Thus, it is impossible for the network to identify between thePS call and the non-PS call, and thus it is impossible for the networkto perform the access control to be identified for each call. Further,it is impossible to make it differentiate for degree of emergency of asubsequent network operation to serve the call in addition to the accesscontrol whether it is the PS call or the non-PS call.

Further, let's assume that the terminal enters within the networkcoverage, and the terminal needs to perform the announcement urgently.In this case, the terminal should be able to perform the RRC connectionestablishment with the network in order to perform the announcement, andit should be able to perform the announcement based on the configurationof the network. However, the network cannot know that the terminal isperforming the RRC connection establishment procedure since it isrequired to perform this urgent announcement. This is because as shownin the table 3, in a prior art, there is no RRC connection establishmentcause value indicating the call for the announcement. Thus, the RRCconnection establishment for the announcement of resource pool may bedelayed, and thus it may result in the D2D operation to be stopped.

In the present invention, to solve this issue, it is proposed to give apriority for the RRC connection establishment to inform the network ofthe necessity of the announcement, or the RRC connection establishmentprocedure for performing the announcement. That is, the RRC connectionestablishment attempt to inform the necessity of the announcementrelated to communication for the public safety (PS), may be handled asthe PS (public safety) call.

If the necessity of the announcement is not related to the PScommunication, then the RRC connection establishment attempt for theannouncement may be handled as the non-PS call.

If the corresponding call is handled as the PS call, the terminalapplies the access control applicable to the PS call. The access controlmay be a service specific access control (S SAC) or an applicationspecific congestion control for data communication (ACDC) for datacommunication.

Similarly, the method may be also applicable to RRC connectionestablishment for the announcement of resource pool configured by thenetwork. That is, if the announcement is required for the communicationfor the public safety, then the RRC connection establishment attempt forthe announcement may be similarly handled as the PS call. Or, if theannouncement is not related to the communication for the public safety,then the RRC connection establishment attempt for the announcement maybe similarly handled as the non-PS call.

If the corresponding call is handled as the PS call, then the terminalapplies the access control applicable to the PS call. The access controlmay be a service specific access control (SSAC) or an applicationspecific congestion control for data communication (ACDC) for datacommunication.

Meanwhile, ProSe direct communication (D2D communication) standardtechnology in 3GPP Rel-12 is specifically introduced for the publicsafety communication and it is applicable to a Vehicle-to-vehicle (V2V)communication service for public safety. The V2V service is an exampleof V2X (Vehicle to everything) service, the V2X service implies aservice in which a vehicle communicates with other persons/things andthus makes its purpose to maximize public safety and/or provideconvenient services. A call for V2X emergency safety service may beconsidered as the above mentioned PS call and thus it may be referred toas the V2X PS call. The service, for which the emergency communicationis not required, despite of the V2X service, may be considered as thenon-PS call, and thus it may be referred to as the V2X non-PS call.

In below, in order for the network to identify between the PS call andthe non-PS call, it is explained that the terminal provides the networkwith the information to identify a call based on any one of thefollowing methods A, B, C. As mentioned above, the call for the RRCconnection establishment to inform the network of the necessity of theannouncement or the call for the RRC connection establishment to performthe announcement is handled as the PS call, or the other call is handledas the non-PS call.

I. Method A

In the method A, the terminal identifies the PS call and the non-PS callat a higher layer such as a NAS layer, the higher layer of the terminal,e.g., the NAS layer may provide different information to a lower layer,an AS layer, based on whether the call is the PS call or the non-PScall. However, the same RRC establishment cause value may be mapped tothe PS call and the non-PS call.

The terminal may provide the network with additional information(indicator) with which the network may identify whether thecorresponding call is the PS call or the non-PS call. This additionalinformation (indicator) may be included in the RRC connection setupcomplete message. Or, the additional information (indicator) may beincluded in an extension field of the RRC connection setup requestmessage.

FIG. 22 represents an operation method of the terminal in accordancewith an embodiment of the present invention.

Referring to FIG. 22, the terminal configures the same existing RRCconnection establishment cause value to the PS call and the non-PS call,and transmits the RRC connection request message including the causevalue to the base station (S141).

In response to the RRC connection request message, the base stationtransmits the RRC connection setup message (S142).

The terminal transmits to the base station, the connection setupcomplete message including the indicator capable of identifying the PScall and the non-PS call (S143).

That is, the terminal uses identically a specific value of the existingRRC establishment cause value for both the PS call and the non-PS callin the RRC connection request message, and may provide by additionallyincluding the information capable of identifying the PS call and thenon-PS call in the RRC connection setup complete message.

The method A may be classified as the following embodiments 1, 1-1, 2,and 2-2.

Embodiment 1

In the embodiment 1, the terminal uses identically the existing RRCestablishment cause value for both the PS call and the non-PS call, andif the corresponding call is the PS call, then the informationindicating the PS call may be further provided.

The terminal may be operated for the PS call in the following manner.Firstly, the terminal configures the RRC establishment cause value as avalue to be provided by the higher layer such as the NAS layer. The RRCestablishment cause value provided by the higher layer may be the sameas any one of the existing RRC establishment cause values shown in Table3.

The terminal additionally provides the network with the informationindicating that the corresponding call is the PS call. This informationmay be provided in the RRC connection establishment process, and forexample, the information indicating the PS call may be provided in theRRC Connection Setup Complete message (RRCConnectionSetupCompletemessage).

When the terminal additionally provides the network with the informationindicating that the corresponding call is the PS call, one bit indicatormay be included to indicate that the corresponding call is the PS call.Or, the indicator indicating a specific purpose of the PS call (e.g.,purpose for the V2X PS service) may be included in the RRC connectionestablishment process, e.g., the RRC connection setup complete message.

The terminal may be operated for the non-PS call in the followingmanner. Firstly, the RRC establishment cause value is configured as avalue provided by the higher layer. The value provided by the higherlayer may be the same as any one of the existing RRC establishment causevalue to be used for the PS call. That is, the same existing RRCconnection establishment cause value is used for the PS call and thenon-PS call.

The terminal may explicitly provide the network with the informationindicating that the corresponding call is the non-PS call. For example,the information indicating the non-PS call may be provided to beincluded in the RRC Connection Setup Complete message(RRCConnectionSetupComplete message).

Or, the terminal does not transmit the information with which it mayidentify whether the corresponding call is the PS call or the non-PScall, and thus it may indirectly (implicitly) inform the network thatthe corresponding call is the non-PS call. When the information that thecorresponding call is the PS call is not included in the RRC connectionsetup complete message, the network may consider the corresponding callthe non-PS call.

Embodiment 1-1

In the embodiment 1-1, the terminal identically uses the existing RRCestablishment cause value for both the PS call and the non-PS call, andif the corresponding call is the non-PS call, then the informationindicating the non-PS call may be further provided.

That is, in the embodiment 1, if the corresponding call is the PS call,then the terminal additionally provides the information indicating thePS call, whereas in the embodiment 1-1 unlike the embodiment 1, if it isthe non-PS call, then the information indicating the non-PS call is tobe additionally provided.

According to the embodiment 1-1, the terminal may be operated for the PScall in the following manner.

Firstly, the RRC establishment cause value is configured as a value tobe provided by the higher layer. The value to be provided by the higherlayer may be the same as any one of the existing RRC establishment causevalue. For example, the PS call may have the RRC establishment causevalue such as the ‘emergency,’ or the ‘high priority access(highPriorityAccess)’ etc.

The terminal does not include in the RRC connection setup completemessage, the information capable of identifying whether thecorresponding call is the PS call or the non-PS call, and thus it may beindirectly (implicitly) informed to the network that the correspondingcall is the PS call. If the information that the corresponding call isthe PS call is not included in the RRC connection setup completemessage, then the network may consider the corresponding call the PScall. Or, the terminal may further provide the network with theinformation indicating that the corresponding call is the PS call.

The terminal may be operated for the non-PS call in the followingmanner.

Firstly, the RRC establishment cause value is configured as a value tobe provided by the higher layer value. The value to be provided by thehigher layer value may be the same as any one of the existing RRCestablishment cause values to be used for the PS call.

The terminal may explicitly provide the network with the informationindicating that the current call is the non-PS call. For example, theinformation indicating the non-PS call may be transmitted to be includedin the RRC connection Setup complete message(RRCConnectionSetupCompletemessage).

Embodiment 2

In the embodiment 2, the terminal uses the same RRC establishment causevalue for the PS call and non-PS call, and may use not the existing RRCestablishment cause value but a newly defined RRC establishment causevalue.

If the corresponding call is the PS call, then the terminal may furtherprovide the information indicating the PS call.

As explained in detail, the RRC establishment cause value is configuredas a valued to be provided by the higher layer, which may be not theexisting RRC establishment cause value but a newly defined RRCestablishment cause value. For example, the higher layer of terminal mayidentically use not the existing RRC establishment cause value such asthe ‘emergency,’ and the ‘a high priority access (highPriorityAccess),’etc. but the new RRC establishment cause value indicating ‘a proximateservice (ProSe)’ for the PS call and non-PS call. As another example,the higher layer of the terminal may identically use the new RRCestablishment cause value indicating the V2X service for a call for theV2X service corresponding to the V2X PS service and the V2X non-PSservice.

The network cannot identify whether the corresponding call is the PScall or the non-PS call only based on the RRC establishment cause valuesuch as the ‘proximity service (ProSe)’ or the V2X service and thus theterminal may provide the network with the information with which it canidentify whether the corresponding call is the PS call or the non-PScall in the RRC connection establishment procedure. For example, theterminal may transmit to be included in the RRC connection setupcomplete message, the information with which it can identify whether thecorresponding call is the PS call or the non-PS call.

According to the embodiment 2, the terminal may operate for the non-PScall in the following manner.

Firstly, the RRC establishment cause value is configured as the value tobe provided by the higher layer. In this case, the value to be providedby the higher layer may be not the existing RRC establishment causevalues but a newly defined value. For example, the higher layer of theterminal may use not the existing RRC establishment cause value such asthe emergency or the highPriorityAccess etc. but the RRC establishmentcause value indicating the ProSe.

The terminal does not include in the RRC connection setup completemessage, the information capable of identifying whether thecorresponding call is the PS call or the non-PS call, and thus it may beindirectly (implicitly) informed to the network that the correspondingcall is the non-PS call. If the information that the corresponding callis the PS call is not included in the RRC connection setup completemessage, then the network may consider the corresponding call the non-PScall.

Or, the terminal may further explicitly provide the network with theinformation indicating that the corresponding call is the non-PS call.For example, the information indicating the non-PS call may betransmitted to be included in the RRC connection setup complete message(RRCConnectionSetupComplete message). That is, if it is the PS call,then the information indicating the PS call is included in the RRCconnection setup complete message, and if it is the non-PS call, thenthe information indicating the non-PS call is included in the RRCconnection setup complete message.

Embodiment 2-1

In the embodiment 2-1, the terminal identically uses the existing RRCestablishment cause value or a newly defined RRC establishment causevalue for the PS call and the non-PS cal, and if the corresponding callis the non-PS call, then the information indicating the non-PS call maybe further provided to the network.

The terminal may be operated for the PS call in the following manner.

Firstly, the RRC establishment cause value is configured as the value tobe provided by the higher layer. In this case, the value to be providedby the higher layer may be the existing RRC establishment cause valuesor a newly defined value. For example, the higher layer of the terminalmay use the existing RRC establishment cause value such as the emergencyor the high priority access (highPriorityAccess) etc. or the RRCestablishment cause value indicating the ‘proximity service (ProSe)’.

For any case, the network cannot identify whether the corresponding callis the PS call or the non-PS call only based on the RRC establishmentcause value.

The terminal may not provide the network with the information capable ofidentifying whether the corresponding call is the PS call or the non-PScall for the PS call in the RRC connection establishment procedure. Forexample, the terminal may not include in the RRC connection setupcomplete message, the information capable of identifying whether thecorresponding call is the PS call or the non-PS call.

On the other hand, for the non-PS call, the terminal may provide thenetwork with the information indicating that the corresponding call isthe non-PS call, being included in the RRC connection setup completemessage.

That is, according to the embodiment 2-1, the terminal may be operatedfor the non-PS call in the following manner. Firstly, the RRCestablishment cause value is configured as the value to be provided bythe higher layer. In this case, the value to be provided by the higherlayer may be the existing RRC establishment cause values or a newlydefined value. For example, the higher layer may provide the existingRRC establishment cause value such as the emergency or thehighPriorityAccess etc. or a new RRC establishment cause valueindicating a Prose-enabled PS call. The terminal may explicitly providethe network with the information indicating that the current call is thenon-PS call. For example, the information indicating the non-PS call maybe transmitted to be included in the RRC connection setup completemessage (RRCConnectionSetupComplete message).

If the above mentioned method A is used, the network can not identifybetween the PS call and non-PS call only based on the RRC connectionestablishment cause value. The network receives the information capableof identifying between the PS call and non-PS call, or confirms in theabsence of the information, and thus it can identify whether thecorresponding call is the PS call or the non-PS call.

II. Method B

In the method B, the PS call and the non-PS call may be identified inthe higher layer. That is, the higher layer such as the NAS layer of theterminal provides the lower layer such as the AS layer with informationdifferent from each other for the PS call and the non-PS call.Difference from the method A is that different RRC establishment causevalues are mapped to the PS call and the non-PS call.

For example, for the PS call, the emergency may be configured for theRRC establishment cause value, whereas, for the PS call, the mo-Data maybe configured for the RRC establishment cause value.

Or, for the PS call, the highPriorityAccess may be configured for theRRC establishment cause value, whereas, for the non-PS call, the mo-Datamay be configured for the RRC establishment cause value.

Or, for the PS call, not the existing values but a newly defined value,e.g., the cause value of ‘ProSe’ may be configured for the RRCestablishment cause value, whereas, for the non-PS call, the mo-Data maybe configured for the RRC establishment cause value.

Or, for the PS call, not the existing values but a newly defined value,e.g., the cause value of V2X may be configured for the RRC establishmentcause value, whereas, for the non-PS call, the mo-Data may be configuredfor the RRC establishment cause value.

If the method B is used and the network receives the RRC establishmentcause value, then it may be identified whether the corresponding call isthe PS call or the non-PS call. However, it is not excluded that avarious type of call is mapped to the same RRC establishment causevalue, and in this case, the various type of call cannot be identified.For example, if the PS call and Prose-enabled emergency call is mappedto the same RRC establishment cause value (emergency call), then thenetwork cannot identify whether the corresponding call is the PS call orthe Prose-enabled emergency call.

III. Method C

In the method C, the PS call and the non-PS call is identified in thehigher layer. Further, different RRC establishment cause values aremapped to the PS call and the non-PS call, and the terminal mayadditionally provide the network with information with which differentpurposes/uses of PS call are identified. That is, in the method 3, thePS call is more classified into and thus the information is to beadditionally provided to the network, indicating explicitly whether thePS call is any one among the Prose-enabled PS call, the V2X PS call, orthe Prose-disabled PS call, or the ProSe based V2X PS call, or non ProSebased V2X PS call. Or, the terminal may provide the network with anindicator with which the call by the existing RRC connectionestablishment cause value and the PS call may be identified.

FIG. 23 represents an operating method of the terminal in accordancewith another embodiment of the present invention.

Referring to FIG. 23, the terminal transmits the RRC connection requestmessage including different existing RRC connection establishment causevalues for the PS call and the non-PS call (S151).

The base station transmits the RRC connection setup message to theterminal (S152).

The terminal transmits the RRC connection setup complete messageincluding an indicator with which the call by the existing RRCconnection establishment cause value and the PS call may be identified(S153).

The method C may be variously applicable to the following embodiment 1,2, and 3.

Embodiment 1

In the embodiment 1 of the method C, the terminal configures theemergency of the existing RRC establishment cause value for the PS call.If the network receives the emergency of the RRC establishment causevalue, then the network cannot identify that the corresponding call isthe PS call. Thus, the terminal may additionally provide the networkwith the information that the corresponding call is the Prose-enabled PScall. The information may be included in the RRC connectionestablishment complete message.

The terminal configures the mo-Data of the existing RRC establishmentcause value for the non-PS call. Additionally, the terminal may notprovide the network with the information indicating that thecorresponding call is the PS call or the non-PS call. Or, the terminalmay provide the information indicating that the corresponding call isthe non-PS call.

Embodiment 2

In the embodiment 2 of the method C, the terminal configures the‘highPriorityAccess’ of the existing RRC establishment cause value forthe PS call. The terminal may additionally provide the network with theinformation that the corresponding call is the PS call. The informationmay be provided in the RRC connection establishment process, and forexample, may be included in the RRC connection establishment completemessage.

The terminal configures the mo-Data of the existing RRC establishmentcause value for the non-PS call. Additionally, the terminal does notprovide the network with the information indicating whether thecorresponding call is the PS call or the non-PS call. Or, the terminalmay provide the network with the information indicating that thecorresponding call is not the PS call.

Embodiment 3

In the embodiment 3 of the method C, the terminal may use not theexisting RRC establishment cause value but a newly defined RRCestablishment cause value for the PS call. For example, the new RRCestablishment cause value indicates the ‘ProSe.’ Further, the terminalmay additionally provide the network with information that thecorresponding call is the PS call. The information may be provided inthe RRC connection establishment process, and for example, may beincluded in the RRC connection establishment complete message.

The terminal configures the mo-Data of the existing RRC establishmentcause value for the non-PS call. Additionally, the terminal does notprovide the network with the information indicating whether thecorresponding call is PS call or the non-PS call. Or, the terminal mayprovide the network with the information indicating that thecorresponding call is the non-PS call, or the information indicatingthat the corresponding call is the Prose-enabled non-PS call.

If the above mentioned method C is used, then the network may identifybetween the PS call and non-PS call only based on the RRC connectionestablishment cause value. However, if various types of call are mappedto the same RRC establishment cause value, then the various types ofcall may not be identified. For example, if the PS call and theProse-enabled emergency call (emergency call) is mapped to the same RRCestablishment cause value (emergency call), then the network cannotidentify that the corresponding call is the PS call or the Prose-enabledemergency call. In this case, the network may identify based on theinformation indicating any one among various types of calls, or mayidentify any one among various types of calls by recognizing in theabsence of the information.

In the explanation of the present invention, the PS call and the non-PScall is mainly explained, but it is not limited thereto. That is, thoughthe present invention has been triggered at the same application layeror service layer, but it may be applicable to identify various types ofcall requiring a different access control or different QoS. For example,it may be applicable to identify between the PS call by the MCPTT(Mission Critical Push To Talk) application and other general call(non-PS call).

FIG. 24 is a block diagram representing the terminal in which theembodiment of the present invention is implemented.

Referring to FIG. 24, the terminal 1100 includes a processor 1110, amemory 1120 and a RF unit (radio frequency unit) 1130. The processor1110 implements the suggested function, process, and/or method. Forexample, the processor 1110 transmits the information informing thenecessity of the control message transmission among the terminal, andreceives a configuration on the control message transmission among theterminal. Further, the processor 1110 transmits the control messageamong the terminal to the other terminal based on the configuration.

The RF unit 1130 is coupled with the processor 1110, and transmitsand/or receives a radio signal.

The processor may include Application-Specific Integrated Circuits(ASICs), other chipsets, logic circuits, and/or data processors. Thememory may include Read-Only Memory (ROM), Random Access Memory (RAM),flash memory, memory cards, storage media and/or other storage devices.The RF unit may include a baseband circuit for processing a radiosignal. When the above-described embodiment is implemented in software,the above-described scheme may be implemented using a module (process orfunction) which performs the above function. The module may be stored inthe memory and executed by the processor. The memory may be disposed tothe processor internally or externally and connected to the processorusing a variety of well-known means.

What is claimed is:
 1. A method for transmitting a resource poolannouncement in a wireless communication system, the method performed bya first user equipment (UE) and comprising: transmitting, to a network,resource pool announcement necessity information; receiving from thenetwork, a configuration for the resource pool announcement in responseto the resource pool announcement necessity information; andtransmitting, to a second UE, the resource pool announcement based onthe configuration, wherein the resource pool announcement necessityinformation informs the network that the first UE, which is in a networkcoverage, must transmit the resource pool announcement to the second UEwhich is out of the network coverage, and wherein the resource poolannouncement indicates at least one of a plurality of resources which isused for transmitting a device-to-device (D2D) signal in the networkcoverage.
 2. The method of claim 1, wherein the resource poolannouncement further indicates the second UE of information required toperform a relay function by the first UE between the second UE and thenetwork.
 3. The method of claim 1, wherein the resource poolannouncement necessity information is transmitted via a radio resourcecontrol (RRC) message.
 4. The method of claim 1, wherein the resourcepool announcement is a control message to be used for public safety. 5.The method of claim 1, further comprising: transmitting to the network,information indicating that the resource pool announcement is no longerrequired.
 6. A user equipment (UE), the UE comprising: a transceiver;and a processor, operatively coupled to the transceiver, wherein theprocessor is configured to: control the transceiver to transmit, to anetwork, resource pool announcement necessity information; control thetransceiver to receive from the network, a configuration for theresource pool announcement in response to the resource pool announcementnecessity information; and control the transceiver to transmit, to asecond UE, a resource pool announcement based on the configuration,wherein the resource pool announcement necessity information informs thenetwork that the first UE, which is in a network coverage, must transmitthe resource pool announcement to the second UE which is out of thenetwork coverage, and wherein the resource pool announcement indicatesat least one of a plurality of resources which is used for transmittinga device-to-device (D2D) signal in the network coverage.
 7. The UE ofclaim 6, wherein the resource pool announcement further indicates thesecond UE of information required to perform a relay function by thefirst UE between the second UE and the network.
 8. The UE of claim 6,wherein the resource pool announcement necessity information istransmitted via a radio resource control (RRC) message.
 9. The UE ofclaim 6, wherein the resource pool announcement is a control message tobe used for public safety.
 10. The UE of claim 6, wherein the UE furthertransmits to the network, information indicating that the resource poolannouncement is no longer required.